Prior art hard magnetic disk drives have enjoyed widespread popularity as mass storage devices for personal computers. Hard disk drives are also referred to as fixed disk drives, rigid disk drives, and Winchester drives.
A rigid disk drive system typically includes a stack of disks mounted on a spindle. The disks are rotated by a motor. The disks reside inside an enclosure.
A transducer is typically used to read digital information from a rigid disk and to write digital information to the rigid disk. A transducer is also referred to as a magnetic head, a Winchester head, or simply as a head. A transducer is typically mounted at the end of a suspension attached to an arm of an actuator. A suspension is also referred to as a flexure.
FIG. 1 illustrates one prior art actuator 2. Actuator 2 pivots about a spindle (not shown) that is inserted into bearing assembly 3. Actuator 2 includes armset 4, suspensions 6, transducers 5, counterweights 7 and 11, steel sleeve buffer 8, and magnetic structure 15. Armset 4 includes arms 13 as part of the body of armset 4. Suspensions 6 provide flexible mounts for the respective transducers 5.
In one prior art rigid disk drive, rigid disks (not shown) reside between pairs of arms 13. Voice coil 15 interacts with a magnet or magnets (not shown) to cause actuator 2 to rotate about a spindle (not shown) inserted into bearing assembly 3. The rotation of actuator 2 causes transducers 5 to move across the respective disks.
Digital information is written in circular tracks on the disks. The rotation of actuator 2 causes transducers 5 to move from track to track. In this way, digital information is written to and read from the disk tracks.
The rigid disk drive also includes electronic amplification circuitry (not shown) that amplifies signals sent by transducers 5. The disk drive also includes electronic control circuitry (not shown) that controls the positioning of the actuator. This control circuitry helps to place the heads or transducers over the desired tracks and helps to minimize track misregistration.
The design of the armset is important to the overall performance of the disk drive because it is the armset that positions the heads over the disks. The armset typically is made of a nonmagnetic material that is strong, yet lightweight. It typically is important that the material be nonmagnetic so as not to interfere with the magnetic reading/writing process. The armset should be strong enough to withstand frequent sudden movements. The armset should be relatively lightweight so that it can be moved quickly given a fixed amount of power for its movement. In other words, low inertia is typically important for an armset.
One reason that it is important that the armset have low inertia is to reduce the access time. The access time is defined as the time required to physically position each head to the exact place where the desired data is stored on the disk and the time to settle on track. The quicker the armset can be moved, the less time it takes to provide the requested data to the user.
Low inertia also often reduces power consumption. It requires less power to move and stop an armset having low inertia versus one having high inertia. Power consumption is often an important design parameter for disk drives installed in battery-powered laptop computers.
It is often preferable that the armset have a high stiffness to mass ratio. The higher the ratio, the higher the inherent frequency. A high inherent frequency often reduces the settling time. After an armset moves to a position and stops, the armset typically vibrates. A high stiffness to mass ratio typically reduces the amplitude of this vibration. A high stiffness to mass ratio typically reduces the settling time.
In the prior art, armsets have been constructed of aluminum in view of the design parameters mentioned above. Aluminum is also relatively inexpensive and easy to machine.
Aluminum armsets, however, have often given way to prior art magnesium armsets because magnesium typically has a higher stiffness to mass ratio and is less dense. Magnesium generally has low inertia. Consequently, magnesium armsets typically are associated with faster access times than comparable aluminum armsets.
Nevertheless, certain prior art magnesium armsets have disadvantages. One disadvantage is that a typical prior art magnesium armset has a coefficient of thermal expansion twice that of the steel bearing assembly connected to the armset. This thermal mismatch typically leads to undesirable stresses and distortions.
FIG. 1 shows a perspective view of one prior art magnesium armset 4. In order to minimize these thermal-induced stresses and distortions, a steel sleeve buffer 8 is used. Steel sleeve buffer 8 resides between armset 4 and steel bearing assembly 3. For one prior art magnesium armset, steel sleeve 8 was coated with a layer of tungsten disulfide to lower the coefficient of friction between the sleeve and armset.
One disadvantage is that steel sleeve 8 typically increases the mass of armset 4, thereby increasing the inertia of armset 4 and decreasing the access time. A further disadvantage of steel sleeve 8 coated with tungsten disulfide is the extra expense of having such a coating.
Another problem associated with thermal expansion is that of thermal misregistration. Metals typically expand as their temperatures are raised. This expansion can often cause transducers to be misaligned with the disk tracks, thereby creating problems in reading and writing data. Many prior art methods address this issue, some mechanical or electrical in nature. Some methods include a reliance on software.
Another disadvantage of a typical prior art magnesium armset is that the magnesium armset typically must be relatively thick to withstand the shock of movement. This thickness adds to the weight of the armset. As a consequence, at least one counterweight is typically required to balance the weight of the armset. FIG. 1 shows two lead counterweights 7 and 11 for armset 4.
Moreover, the fact that a typical magnesium armset is relatively thick means that there are fewer arms for a given height of an armset. This means that the drive can accommodate fewer disks for a given height of an armset.
A further disadvantage of a typical prior art magnesium armset is that given its inherent properties, disk drive access times of less than 10 milliseconds are hard to achieve.
Beryllium has been used in the prior art as an aerospace structural material and as a moderator and reflector in nuclear reactors. Among the metals beryllium, magnesium, aluminum, titanium, and steel, the two metals that are the least dense are beryllium and magnesium. Among the metals beryllium, magnesium, aluminum, titanium, and steel, the metal beryllium has the highest modulus of elasticity. Beryllium also has a moderate tensile strength. Additionally, beryllium is relatively resistant to corrosion and has a relatively high melting point.
One disadvantage of beryllium is its high cost. Another disadvantage is that the machining of beryllium is relatively difficult and expensive.